Electrical apparatus



Oct. 17, 1939. R. J. ELSOME-JONES ELECTRI CAL APPARATUS Filed May 19, 1938 FIGI.

IN VEN Tole lE'oNnLD 3'08 ELSoHraoNts HIS HTTOENE Y.

Patented Oct. 17, 1939 PATENT OFFICE ELEGTRIUAL APPARATUS Ronald Job Elsome-Jones, London, England, assignor to Technical Inventions Limited, London, England Application May 19, 1938, Serial No. 208,919 In Great Britain May 21, 1937 6 Claims. (Cl. 175-364) This invention relates to apparatus for obtaining alternating current from a direct current source and has more especial reference to apparatus for obtaining high tension alternating current from low tension direct current, although the invention is not limited in this respect since, by employing a step-down transformer, low tension alternating current may be obtained from higher tension direct current.

10 In co-pending application Serial No. 127,248

apparatus of this character is described comprising a transformer the core whereof has pole pieces between which is mounted a rotor having an associated circuit breaker interposed in the primary circuit of the transformer and including a commutator with a number of live segments corresponding with the poles of the rotor and a slip ring with co-operating brushes.

Hitherto it has been the practice to endeavour to reduce sparking and consequent burning of the contacts in circuit breakers, buzzer commutators and the like, by shunting across such contacts a small capacity paper or like condenser and, while this has provided a partial g remedy slightly reducing the sparking in the case of small currents, it has limited the utility of the device in which it is present to cases capable of being dealt with by small current inputs, the more so since it has been found that in appago ratus of the kind mentioned .the peak current in the primary circuit is considerably in excess of the mean current flowing. 7 Moreover, with paper and like condensers as hitherto commonly used, the discharge is sub- 7 335 stantially incomplete and there is a residual winding of the transformer in apparatus for obtaining alternating current from a direct current sourceis bridged by a reversible electrolytic condenser the reactance of which gives it a charge 'value approximately equal to the difference beu tween the mean current and the peak current flowing in the primary circuit, which electrolytic condenser is not only operative to eliminate or substantially reduce sparking, but .also to improve the wave form of the output, as hereafter described. That is to say, the reactance of the 5 condenser at the frequency of operation is so related to the inductance of the primary circuit, that current in excess of normal is taken by the condenser and discharged during the interrupted phase. Thus the term charge value as used 1 in this specification is intended to refer to the charge which the condenser is capable of receiving and is proportional to the reactance of the condenser at the frequency of the circuit.

For instance, in apparatus of the kind de- 15 scribed in the aforementioned co-pending application, with a direct current supply of 5 amperes at 12 volts the peak current may be 9-10 amperes and for such an apparatus according to the present invention, an electrolytic con- 20 denser of a capacity of about 400 microfarads and charge value of L5 amperes is shunted across the primary winding, being effective to absorb the peak current and give an alternating current output of satisfactory Wave form.

Alternatively, the reversible electrolytic condenser may be interposed in the primary circuit between one terminal of the primary winding and the circuit breaker i. e., in series with the primary winding the capacity of the series con- 80 denser being correlated with the peak current of the motor field circuit and being, for instance, 1,000 microfarads for a peak current of 8 amperes.

A reversible electrolytic condenser, i. e., one having an oxide film on each electrode is employed, owing to the liability of polarized electrolytic condensers to break down under alternating potential, advantageously although not necessarilyin conjunction with a condenser bridging the interrupter contacts or commutator brushes and it will be understood that the present invention is not limited to apparatus according to the aforementioned application No. 127,248, but may also be usefully employed where a separate motor driven interrupter is interposed in the primary circuit of the transformer.

Conveniently, however, according to another feature of the invention, the commutator of the motor fulfills the function of circuit interrupter for the primary of the transformer, a common brush system being employed.

Reference will now be had to the accompanying drawing which shows the circuits of two specific embodiments of converting apparatus of the kind last mentioned,

Fig. 1 illustrating an arrangement where the condenser is in parallel with the primary winding of the transformer, and

Fig. 2 an alternative arrangement where the condenser is in series with the transformer primary.

In the drawing, referring first more particularly to Fig. 1, the circuit for instance being adapted for lighting a neon sign from a 6 or 12 volt accumulator, l indicates the core of the transformer, 2 the primary winding thereof, 3 the secondary winding which may be centre tapped to ground, and 4 the accumulator. The motor interrupter comprises a repulsion motor 5 and fixed for rotation with the rotor thereof a commutator 6 having a brush I and a slip ring 8 having a brush 9 connected in series with the primary winding 2 across the terminals of the accumulator 4. The field winding IQ of the motor 5 is shunted across the primary winding 2 so that the commutator 6 serves both to control the motor and to interrupt the primary current.

The commutator and slip ring brushes 1 and 9 respectively are bridged by an electrolytic condenser H of 25 microfarads and the primary winding 2. is furnished according to the invention with a shunt condenser ll which is a reversible electrolytic condenser having a capacity of from 800-1,000 microfarads according to the peak amperage of the primary circuit and the output required.

A suitable form of reversible electrolytic condenser comprises an aluminium electrode having a double electrolytic film or two unit condensers with their polarities opposed and coupled in parallel may be employed.

In Fig. 2 the shunt condenser 12 is replaced by a series electrolytic condenser l2a between the field winding ll] of the motor 5 and the transformer primary 2, the condenser l2a also having a capacity of, say, EMU-1,000 niicrofarads so as to have a charge value approximately equal tothe difference between the mean current and the peak current flowing in the primary circuit.

Where a low voltage alternating current output is required, a step down transformer may be employed, as will be understood.

Moreover, as aforementioned, a separate motor may be employed in place of the combined motor and interrupter, or the unit transformer with built-in motor, as described in co-pending application Serial No. 127,248, may be used.

By the present invention improved, economical and efficient apparatus for obtaining alternating current from a source of direct current supply is obtained.

What I claim is:

1. Apparatus of the kind specified for obtaining alternating current from a direct current source, comprising a transformer and an interrupter or circuit breaker for the primary circuit thereof, having a reversible electrolytic condenser associated with the primary winding of the transformer, the reactance of the condenser being such that its charge value is approximately equal to the difference between the mean current and the peak current flowing in such primary circuit.

2. Apparatus of the kind specified for obtaining alternating current from a direct current source, comprising a transformer and a motor driven interrupter or circuit breaker for the primary circuit thereof, a brush and commutator system common to said motor and interrupter, and reversible electrolytic condenser in the primary circuit between the primary winding and the circuit, breaker, the capacity of the series condenser being such that its charge value is approximately equal to the difference between the mean current and the peak current flowing in such primary circuit.

3. Apparatus according to claim 1 wherein the field winding of the motor, the primary winding and the electrolytic condenser are in parallel and are connected to a source of direct current supply through the motor driven interrupter.

4:. Apparatus according to claim 2 including a second condenser bridging the circuit breaker.

5. Apparatus of the kind specified comprising a transformer, the core whereof has pole pieces between which is mounted a rotor having an associated circuit breaker interposed in the primary circuit of the transformer, wherein a reversible electrolytic condenser bridges the primary winding of the transformer, the capacity of the condenser being such that its charge value is approximately equal to the difference between the mean current and the peak current flowing in such primary circuit.

6. Apparatus of the kind specified comprising a transformer, a motor driven interrupter for the primary circuit of said transformer including a rotor and a commutator with a number of live segments corresponding with the poles of the rotor, a slip ring, and co-operating brushes for said commutator and slip ring, wherein the primary circuit also includes in series with the commutator a reversible electrolytic condenser having a capacity such that its charge value is approximately equal to the difference between the mean current and the peak current flowing in such primary circuit.

RONALD JOB ELSOME-J ONES. 

